The present invention relates to an ink ejection printing apparatus comprising means for automatically preventing clogging of an ink ejection orifice.
Printers are presently being developed for use in facsimile systems and the like which utilize the principle of ink ejection. An ink ejection head formed with a tiny ink ejection orifice is moved in a scan direction adjacent to a sheet of copy paper and electrical signals are applied to the head to cause ink ejection onto the copy paper at positions corresponding to dark portions of the image being reproduced. An effective ink ejection head utilizes the electrostrictive effect in which application of an electrical pulse to an electrostrictive plate in the ejection head causes a tiny drop of ink to be ejected which forms a dot on the copy paper. The paper is fed perpendicular to the scan direction to reproduce successive scan lines and ultimately the entire image.
In order to accomplish satisfactory ink ejection, the diameter of the ejection orifice must be extremely small and the ink passageway leading thereto relatively long and narrow. In addition, the ink used must be rather thick in order to provide sufficient contrast for the reproduced image. This configuration, unfortunately, is conducive to drying of the ink in the area of the orifice which results in an ink clog rendering the ejection head inoperative.
Various means have been proposed to prevent such clogging. It has been attempted with unsuccessful results to prevent clogging by recessing the orifice in the ejection head. Another expedient is to provide a cap which the apparatus operator fits on the ejection head after using the apparatus to hermetically seal the orifice.
The latter method, although effective if the operator is careful and conscientious, is disadvantageous in daily practical use. Careless operators often neglect to fit the cap or fit it in a rough manner which causes ink ejection into the cap. This causes a build-up of dried ink in the cap which destroys the hermetic seal rendering the cap useless even if fitted.